Polyisocyanate polyaddition products obtainable by reaction of isocyanates with compounds that are reactive towards isocyanates, e.g. polyols, i.e. compounds having at least two hydroxyl groups, as well as composite elements of these products with other plastics, are generally known. Stressing of these composite elements by high temperatures and humidities often leads to an undesirable separation of the plastics from the polyisocyanate polyaddition products. Particularly when these composite elements are used in automotive construction, for which stressing of this type cannot be ruled out, separation of the polyisocyanate polyaddition products from the other plastics, and thus destruction of the composite element, is unacceptable.
In the production of the composite elements, and particularly of the polyisocyanate polyaddition products, the problem can occur that the starting components, particularly the polyol component, which contains the starting materials that are reactive towards isocyanates, do not give stable mixtures. Precisely at low temperatures, e.g. lower than 20° C., individual polyols may tend to flocculate in the polyol component or to precipitate in the polyol component. It is important to avoid this problem, precisely for the reproducible production of high-quality products.
DE-A 10 022 280 describes a process for the production of composite elements with improved adhesion and humid ageing properties of such composite materials comprising thermoplastics and polyurethanes. The composite is used e.g. to produce instrument panels, these panels conventionally being constructed e.g. of a thermoplastic support, a polyurethane (“PUR”) foam and an additional outer layer of e.g. polyvinyl chloride (“PVC”), thermoplastic polyolefin (“TPO”), acrylonitrile butadiene styrene (“ABS”), thermoplastic polyurethanes, sprayed polyurethane skins etc.
By using isocyanate-polyester prepolymers containing ester groups for the production of polyurethane foams according to DE-A 10 022 280, improved properties are obtained, in particular good adhesion between the thermoplastic and polyurethane foams of this type. When such a composite is stored in humid conditions for up to 80 hours at 80° C. and 80% relative humidity, the composite of thermoplastic and polyurethane foam is intact. After that, however, the composite separates.
Another method of producing composites is shown in EP-A 1 531 173, in which isocyanate-polycarbonate prepolymers are described for the production of polyurethane foams with improved adhesion to other thermoplastics during humid ageing. These polyesters or polycarbonates, which substantially improve the adhesion of PUR foams to thermoplastic supports, have to be used on the isocyanate side as the solubility of these components in the polyether polyols to be used with them is very limited.